The invention relates to a method for the reliable operation of a brake booster system for a braking system of a motor vehicle, particularly a motor vehicle powered by an internal combustion engine, wherein a pressure value prevailing in the brake pressure reservoir of the brake booster system is acquired by means of a pressure sensor. The invention additionally relates to a brake booster system, particularly a vacuum brake booster system, for a vehicle braking system that can be actuated by means of an actuating mechanism. The brake booster system includes a brake pressure reservoir and, associated therewith, a pressure sensor that acquires the pressure value prevailing in the brake pressure reservoir of the brake booster system. The invention is further directed to a circuit for implementing the aforesaid method and for installation in the aforesaid brake booster system.
Motor vehicles, particularly those powered by internal combustion engines, are often provided with braking systems that are equipped with a brake booster system designed to support the muscular energy of the driver with additional energy. In so-called hydraulic brake booster systems, this additional energy is produced by means of an overpressure prevailing in the brake pressure reservoir and delivered by a hydraulic pump. In so-called vacuum brake booster systems, this additional energy is produced by means of an underpressure prevailing in the brake pressure reservoir and generated from the intake tube of the internal combustion engine or delivered by a vacuum pump. For the reliable operation of brake booster systems, a pressure sensor is conventionally built into the brake pressure reservoir to check whether sufficient pressure is present therein. The pressure sensor is connected to a brake pressure control system that increases or decreases the brake pressure in the brake pressure reservoir on the basis of the pressure value measured by the pressure sensor. For example, in a conventional method for operating a vacuum brake booster system, a higher throttle ratio (the intake-tube pressure divided by the pressure before the throttle valve) is requested by the pressure sensor if too low of an under pressure is measured in the brake pressure reservoir. However, this known method has the disadvantage that the brake pressure regulator operates incorrectly if an error occurs in the brake booster system, especially if a defective pressure sensor has been installed in the brake pressure reservoir. It is desirable, however, to be able to ensure adequate pressure for the brake booster system in such cases as well.